Conventional thermal interface media reduce the temperature gradient between two different surfaces in close proximity with one another. The surfaces are typically mating surfaces. The conventional interface media are positioned in the gaps or voids between the two surfaces so that the thermal resistance is lowered thereby allowing the heat to flow away from the hotter surface. The efficient flow of heat will be impeded if any gaps or voids remain at the interface surfaces. Examples of conventional interface media are thermal grease and silicone pads (thermal gaskets).
However, existing interface media have some undesirable characteristics. In particular, thermal grease is difficult to apply properly and when applied too thick, the heat transfer performance degrades . Unwanted material, such as machining chips, tend to collect in the grease so that even larger gaps are produced which can also reduce heat transfer performance. In addition, thermal grease cannot be completely removed without leaving a residue even when cleaned with a solvent. Moreover, thermal grease will contaminate solder joints if the grease gets on surfaces that are to be soldered. The conventional thermal gaskets have limited compressability (10% to 20%), and therefore, thick sections of the gasket are required to fill even small voids. Unfortunately, thick thermal gaskets have poor heat transfer qualities.
An example of a conventional thermally conductive gasket is found in U.S. Pat. No. 4,776,602 which issued on Oct. 11, 1988 to Paul E. Gallo. The gasket device includes a metallic core with an upper and lower face. The core is fabricated from tin plated stainless or low carbon steel. A thermally conductive expandable graphite material, such as aluminum foil, contacts with the upper face. A pair of compressible non-asbestos facing layers are disposed on opposing sides of the core and are comprised of clay, rubber and aramid fibers. Tangs are formed in the core to clinch together all the layers in the device.
U.S. Pat. No. 4,485,138, which issued on Nov. 27, 1984 to T. Yamamoto, et al., discloses a heat-resistant sheet gasket for an automobile engine. The gasket includes a thin, metal sheet core surrounded by a flexible elastomer layer. The metal core may be fabricated from cold-rolled steel plate. The layer is fabricated from a milled blend of short rubber fibers, long polymeric fibers and thermally conductive particles to accelerate heat dissipation. Clay fillers may be added to the blend to reinforce the rubber. Pressure is applied to both sides of the metal core to laminate the blend afterwhich the blend is vulcanized.
U.S. Pat. No. 4,451,047, which issued on May 29, 1984 to David P. Herd, et al., discloses a seal for a stem gate valve. The seal includes a pair of frustoconical metal ring gaskets between which two identical make-up rings of Teflon are disposed. The metal ring gaskets may be fabricated from stainless steel or from other metals such as carbon or alloy steel. A core ring of compacted graphite is provided between the make-up rings. A bearing ring is positioned around the inner periphery of the core ring between the core ring and the valve activating stem. The bearing ring is fabricated from a polytetrafluorethylene sold under the trademark TEFLON or a polytetrafluorethylene with molybdenum disulfide sold under the trademark MOLY-TEFLON material. The material for forming the make-up and bearing rings should be sufficiently elastic to flow into any minute gaps existing between the metal ring gaskets and the valve stem and stuffing box.
U.S. Pat. No. 4,428,593, which issued on Jan. 31, 1984 to Robert S. Pearlstein, discloses a gasket assembly for an internal combustion engine. The assembly includes a solid, expensive metal core of cold-rolled steel which has opposed planar sides. A compressible gasket material, which may be fiber reinforced, is laminated to the planer sides. The gasket material may include asbestos, glass fibers, etc. and may also include nitrile, peoprene or polyacrylic elastomers as a binder. Beads of silicone sealant are arranged on the core surfaces beneath the gasket material at those areas where increased sealing forces are expected. A second embodiment discloses a pair of gasket layers formed from the materials used in the aforementioned gasket material. The layers adhere to an elastomeric sealing pattern. Alternatively, the sealing material may include metal, ceramics or plastic preforms. The layers may be bonded closely about the pattern.
As one can ascertain, the above assemblies are relatively complicated, difficult to fabricate and to use. Certain of the devices are relatively thick and inefficient in operation.